Process for the recovery of zinc from its ores.



To all wkom it may concern denser heating of the charge.

ENITED STATES PA'rEN'r OFFICE;

' I apex no rrz'nnm," or ntinnlv, GERMANY.

menace. Noilrawingp Be it known that I,- \iinx ltoirznnrar, a1 subject ot the ,King of Prussia, residing at Di'nen, Rheinl-and, Germany, have invented certain new and useful Improvements in,-

P1-ocesses for the Recovery of Zine'from Its, Ores; and l-do' hereby declare the, "fol lon ingto be alull, clear, and exact descrip tion oftheinvention i t i ,7

My nventwn relatesto the recovery of its recoveryby distillation from :a'reducing agent in areto'rt or m ufile v v The ob3ect of; the-1nvent1on s to prevent chargecontaining the ore-and a reducing as much;' as possible ,th'enformatipn of zinc dus .that i's carried by reducing gases oulsidemtthe reduction zone and mtothe' atmosphere, Where a considerable portion; is losttand said dust also has aharmful a'ctiornonthe' ivorlnnentending tlie"i'etort s. v I have {discovered that the formation of zinc :dust not so much "due to improper condensat' rot the Zinc vapors nithe con.-

a'tter charging the reducing. chamber.

'tn thereduction of'zinc oreslby the use of carbon as a reducing means in niutlles, it has long betin noted that only a very small amount ol -moltenmine? is deposited or collected in the eondensing cliamber-ofthe mullie for some time after charging, say about the first three'to six hears-of the Instead of molten zinc being deposited, the zinc vapors condense to a gray powder, which, although metallic. does not melt at the melting point ot zinc. To order to convert this powder into molten Zinc the ten'iperature must be raised again to the vaporization temperature of zinc. Consequently, the formation of this zine powden or so called zinc dust, is very ohiectionable in processes for the recovery of zinc from its ores, and especially so in the distillation processes, where the reduction is carried out in muflles.

The formatimi of the zinc dust is a source of great loss of metal: much of it is carried out of the condensers by the gases resulting from the heating of the charge; it then becomes oxidized by the oxygen of the air and forms the bluish zinc oxid fumes so destructive to animal and vegetable life about the reduction plant. It has long been a problem to either prevent or reduce the Specificatioirof Letters Patent.

[717. zinc heat treatn1eiit,- moreespecially to,

, equation: as it is to its unavoidable 'formrn' i tion, in the present processes, Immediately rnoonss'ron min-RECOVE Y or zine FROM 132s ones.

formation of this zinc dust in the reduction of zinc ores.

It is Well known. that materially thinning the zinc vapor with other gases greatly increases the formation of zinc dust, and. almost entirely prevents the condensation of the vapors into molten zinc. Ingalls Metal large of Zinc amt Cadmium, 1906, p. 656; Sodin, Mei/allergic du Zinc, 1905, pp. 714:- Thisundesirable result follows especially when the" heat required for the reduction of the ore is supplied by the combustion of aportion of the carbon contained in the charge, whereby largequan'tities of gases of combustion. become mixed with the gases of reduction. It is for this reason, that at the presentday it is impossible to reduce zinc ores in shaft furnaces to obtain molten zinc; The product-of such furnaces is 'zinc dust, only. In the muffle the heating gases cannot mix.- With the gases of reduction.

The process of reduction is carried out in the muffle in accordance with the following Off course the zinc vapor is mixed with the carbon: monoxid; this cannot be avoided under any circumstances. The quantity of CO is, however, very much less than the products of combustion: resulting from heating the charge.

If we observe carefully the reduction process in the mutlie or retort, We Will note that during the first three to six hours after charging, or the beginning of the reduction, the zinc dust formed, and that after this time theformation of zinc dust almost entirely ceases. Observation of this fact has led me'f 'to a solution of the problem for either entirely preventing or almost entirely pre enting the formation of zinc dust. This I do by heating the charge, e. ore and carbon, as usually understood in normal retort practice for the recovery of zinc, before placing said charge in the muffler or retort. I am' of opinion that the result is due to the fact that when the charge is placed in the mutlic or retort in a cold condition, the reduction connnences in the outer portions, of the charge adjacent to or in contact With the hot trails of the retort or muille and before the center of the charge has even be- Zcome Warm. The zinc vapor or fumes pass y Patent edJunelB,i914.

Application meaau 'us 28,1911. Serial No, eieaoi.

theirway to the condenser, condense, and

become suspended as dust in the reduction gases,'and as such enter the condenser, and some ofrthem pass through the condenser, with the gases, into the air. This zinc dust formation continues until the center of the charge becomes sufliciently heated to preven't it which requires considerable time, by reason of the poor heat conductivity of the charge.

After many years of observation and experimenting I have discovered that the preheating-temperature for the charge should be about 600 C., 2'. 6., not below this, and not much above it. That is to say, the limits of temperature are comparatively narrow, say 600. At this low temperature no reduction of zinc can take place, and the temperature is sufiiciently high to prevent the physical alteration of the zinc vapor, At over'700 0., a strong reduction of, zinc ore takesplace, and it is consequently unsuitable to preheat the charge above this point. At 600 C. the condensation of zinc vapors does not take-place, nor does reduction take place at this temperature. Conse.

quently the charge in any case should be heated only between the temperature at which zinc vapor is not condensed and the temperature at which reduction commences. Should the pre-heating of the charge be carried so far as to partly reduce some of the zinc and condense it Within the body of the charge, then when such a charge is placed in the retort the condensed zinc vapors in the form of zinc dust will be carried off as be fore by the reduction gases, and the result aimed at will not be attained. I

My invention comprises either heating the ore separately from the other ingredients of the charge; or heating the mixed charge before it is 'placed in the retort or reducing chamber, to a temperature sufficient to pre vent the described formation of zinc dust. For a mixed charge the temperature should in no case go to or beyond the reduction zinc and below temperature of the ore, which should be not over 600 C., so that it will he certaih that no zinc dust has been formed during this pro-heating period.

The preheating of the charge to about reducing temperature will shorten the time usually required for the reduction of the charge. hen the ore and other ingredients of the charge are heated separately, the preheating may be carried above ($00 but should not be carried so high as to vaporize the values of the ore, or to reduce it.

I am aware that I am not the first to preheat a charge of Zinc orc'hefore charging it into the reducing chamber; such pro-heating, however, has been done at a tci'npeirature unsuitable to accomplish the results attained by my process.

I claim 1. The step in the process of zinc distillation in retorts, which comprises preheating the charge of ore and reducing material to a temperature above the condensation temperature of zinc and below the reducing temperature of the charge.

2. The step in the process of zinc distillation in retorts, which comprises pro-heating the charge of ore to about 600 C. before charging the same, thereby preventing zinc dust formation.

The step in the process of zinc distillawhich comprises separately tion in retorts, pre-heating the constituents of the charge of ore and reducing material to a temperature above the condensation temperature of the reducing temperature of the charge.

In testimony that I claim the foregoing as my invention, I have signed my name in presence of two sul'iscribing witnesses.

ALEX ROITZHEIM.

Witnesses EnwAnn GOTTSCHALK, Josnrn S'ronrEN. 

